Testosterone (T) is a primary androgenic hormone produced in the interstitial cells of the testes and is responsible for normal growth, development and maintenance of male sex organs and secondary sex characteristics (e.g., deepening voice, muscular development, facial hair, etc.). Throughout adult life, testosterone is necessary for proper functioning of the testes and its accessory structures, the prostate and seminal vesicles; for sense of well-being; and for maintenance of libido and erectile potency.
Testosterone deficiency—insufficient secretion of T characterized by low serum T concentrations—can give rise to medical conditions (e.g., hypogonadism) in males. Symptoms associated with male hypogonadism include impotence and decreased sexual desire, fatigue and loss of energy, mood depression, regression of secondary sexual characteristics, decreased muscle mass, and increased fat mass. Furthermore, hypogonadism in men is a risk factor for osteoporosis, metabolic syndrome, type II diabetes, and cardiovascular disease.
Various testosterone replacement therapies (TRTs) are commercially available for the treatment of male hypogonadism. Pharmaceutical preparations include both testosterone and testosterone derivatives in the form of intramuscular injections, implants, oral tablets of alkylated T (e.g., methyltestosterone), topical gels, or topical patches. All of the current T therapies, however, fail to adequately provide an easy and clinically effective method of delivering T. For example, intramuscular injections are painful and are associated with significant fluctuations in serum T levels between doses; T patches are generally associated with levels of T in the lower range of normal (i.e., clinically ineffective) and often cause substantial skin irritation; and T gels have been associated with unsafe transfer of T from the user to women and children. As well, the sole “approved” oral T therapy, methyltestosterone, is associated with a significant occurrence of liver toxicity. Over time, therefore, the current methods of treating testosterone deficiency suffer from poor compliance and thus unsatisfactory treatment of men with low T.
Testosterone and its esters are poorly bioavailable—owing to extensive first pass intestinal and hepatic metabolism—or ineffective—due to an inability of the body to liberate testosterone from its testosterone prodrug. For example, testosterone and testosterone esters with side chains of less than 10 carbons in length are primarily absorbed via the portal circulation resulting in substantial, if not total, first pass metabolism. Fatty acid esters of long carbon chains (i.e., 14 or more carbons) may be absorbed by intestinal lymphatics, but the longer the fatty acid chain length, the slower the rate and extent of hydrolysis of the ester by esterases to liberate testosterone thus resulting in poor (i.e., clinically ineffective) pharmacological activity.
Other than selection of a testosterone ester, the formulation of the testosterone ester presents unique challenges. The gastrointestinal environment is decidedly aqueous in nature, which requires that drugs must be solubilized for absorption. However, testosterone and particularly its esters are extremely insoluble in water and aqueous media, and even if the T or T ester is solubilized initially in the formulation, the formulation must be able to maintain the drug in a soluble or dispersed form without precipitation or, otherwise, coming out of solution in vivo (although such a property can be tested in vitro, for example, by mixing the contents of a formulation in simulated intestinal fluid). Furthermore, an oral T formulation must, effectively release T or T ester according to a desired release profile. Hence, an effective formulation of T or T ester must balance good solubility with optimum release and satisfaction of a targeted plasma or serum concentration profile.
For these reasons, among others, no oral formulation of testosterone or testosterone esters has been approved by the United States Food and Drug Administration (FDA) to date. In fact, the only oral testosterone product ever approved to date by the FDA is methyltestosterone (in which a methyl group covalently bound to a testosterone “nucleus” at the C-17 position to inhibit hepatic metabolism; note, also, that methyltestosterone is not a prodrug of testosterone) and this approval occurred several decades ago. Unfortunately, use of methyltestosterone has been associated with a significant incidence of liver toxicity, and it is rarely prescribed to treat men with low testosterone.
As noted above, fatty acid esters of testosterone provide yet another mode of potential delivery of testosterone to the body (i.e., as a “prodrug”). Once absorbed, testosterone can be liberated from its ester via the action of non-specific tissue and plasma esterases. Furthermore, by increasing the relative hydrophobicity of the testosterone moiety and the lipophilicity of the resulting molecule as determined by its n-octanol-water partition coefficient (log P) value, such prodrugs can be absorbed, at least partially, via the intestinal lymphatics, thus reducing first-pass metabolism by the liver. In general, lipophilic compounds having a log P value of at least 5 and oil solubility of at least 50 mg/mL are transported primarily via the lymphatic system.
Oral formulations of testosterone esters providing clinically-effective serum testosterone levels to treat hypogonadal men (i.e., those with a serum T concentration of ≤300 ng/dL) over an extended period of time are disclosed in WO2011129812, which is incorporated in its entirety by reference.
It has long been recognized that TRT lowers serum high-density-lipoprotein (HDL) and its surrogate value, serum HDL-cholesterol (HDL-C) (Meriggiola, M. C., et al., Int J Androl, 1995. 18(5): p. 237-42; Semmens, J., et al., Metabolism, 1983. 32(5): p. 428-32). Two factors may influence the amount of HDL suppression: route of delivery, and dose. Typical HDL suppression is about 10% with formulations that deliver T levels at the lower end of the physiological range, such as gels. Other formulations such as such injectable testosterone enanthate (TE), implantable subcutaneous TU pellets, and oral TU (Andriol®) have much higher suppression of HDL than gels (up to 37% for pellets). Independent of the mode of delivery, supra-physiological doses of T, such as in athletes abusing anabolic steroids, lead to even higher HDL suppression.
It has also long been recognized that elevated serum levels of HDLc are associated with reduced risk of cardiovascular (CV) disease and its sequelae (Hislop, M. S., et al., Atherosclerosis, 2001. 159(2): p. 425-32). Because TRT lowers HDLc, there has been the concern that TRT may increase the risk of cardiovascular disease (CVD). However, the effect of raising or lowering HDLc on CV risk and mortality has recently come into question based on: a) clinical trials in which raising HDLc did not improve mortality (Toth, P. P., et al., J Clin Lipidol, 2013. 7(5): p. 484-525; Boden, W. E., et al., N Engl J Med, 2011, 365(24): p. 2255-67), but in fact worsened it; and b) based on populations who have very low HDLc, albeit with mutant HDL associated proteins, who have reduced CV risk (Dodani, S., et al., J Clin Lipidol, 2009. 3(2): p. 70-7). Thus due to the complexity of HDL biology that encompasses not only the measurement of total HDLc but also the composition and function of this lipid fraction, there does not seem to be a simple relationship between HDLc serum concentrations and CV risk/mortality. As the functional and compositional complexity of HDL becomes better understood, it has become clear that HDLc is a relatively crude index of CV risk, and the clinical significance of HDLc alone has been increasingly called into question (de Ia Llera-Moya, M., et al., Arterioscler Thromb Vase Biol, 2010. 30(4): p. 796-801; deGoma, E. M., et al., J Am Coll Cardiol, 2008. 51(23): p. 2199-211. 29; Vaisar, T., et al., J Clin Invest, 2007. 117(3): p. 746-56).
The inverse relationship between HDLc and CVD risk has been attributed to its function in reverse cholesterol transport (RCT) and other antiinflammatory or anti-oxidative functions (Toth, P. P., et al., J Clin Lipidol, 2013. 7(5): p. 484-525). The dogma that low HDLc is a therapeutic target has recently been challenged based on negative findings in outcome trials with niacin (Boden, W. E., et al., N Engl J Med, 2011, 365(24): p. 2255-67) and CETP inhibitors. These trials did not show a benefit in raising HDLc, and in fact treatment which raised HDLc had a deleterious effect on CVD risk (Barter, P. J., et al., N Engl J Med, 2007. 357(21): p. 2109-22). Furthermore, normal HDLc levels (men >40 mg/dL and women >50 mg/dL) are present in many patients with CV events, as exemplified in the Framingham study in which about 43% of the CV events occur in patients with low serum levels of low-density-lipoproteins (LDL) and normal levels of HDLc (Dodani, S., et al., J Clin Lipidol, 2009. 3(2): p. 70-7); Annema, W. and von Eckardstein, A., Circ J, 2013. 77(10): p. 2432-48). Finally low HDLc levels associated with mutant Apo-A1 such as Apo-A1 Milano are cardioprotective (Chiesa, G., and Sirtori, C. R., Curr Opin Lipidol, 2003. 14(2): p. 159-63). while other mutations in Apo-A1, ABCA1, and LCAT also lead to low HDLc level but are associated with increased cardiovascular risk (Tietjen, I., et al., Biochim Biophys Acta, 2011. 1821(3): p. 416-24). The conclusion from these observations is that HDLc is a relatively poor measure of HDL functionality and hence CV risk (Annema, W. and von Eckardstein, A., Circ J, 2013. 77(10): p. 2432-48). This has prompted the development of novel metrics of HDL function that may be more sensitive then the absolute level of HDLc in predicting risk. Among these metrics are in vitro CE capacity, pre-particle quantification, and HDL particle fractionation.
An exploratory analysis of the effects of exposure to oral TU or topical T gel on CE capacity and the quantitation of HDL particle numbers and HDL subfractions, demonstrated: 1) a modest but statistically significant drop in mean CE capacity in the oral TU group compared to T gel, but both treatments were associated with a decrease; 2) a decrease in total HDL particle number which was not statistically significant between the two groups; and 3) a redistribution in HDL subclasses in the oral TU group with a significant shift toward very small, more anti-atherogenic, HDL subclass particles (Example 7). This effect may be driven upregulation of hepatic lipase (to which oral T would be exposed upon its passage through the hepatic portal system), which breaks down large, cholesterol-laden HDL particles to smaller preβ-1 and nascent HDL particles, which are very efficient reverse cholesterol transporters through the ABCA1 receptor.
The peroxisome proliferator-activated receptor (PPAR) isoforms are members of the nuclear receptor superfamily of ligand-activated transcription factors. They were first identified in Xenopus frogs as receptors that induce the proliferation of peroxisomes (Dreyer et al. 1992. Cell 68: 879-887). Three PPAR isoforms are known: PPARα, PPARγ, and PPARδ. The PPARs control gene expression by interaction with specific response elements in the promoter region of target genes (Tugwood et al. 1996. Ann. New York Acad. Sci. 804: 252-265). The PPARs play a central role in carbohydrate and lipid homeostasis, and govern other biological processes such as energy metabolism, cell proliferation and differentiation, and inflammation (Chakrabarti and Rajagopalan. 2004. Curr. Med. Chem.: Immunol. Endocr. Metab. Agents 4: 67-73; Escher and Wahli. 2000. Mutation Res. 448: 121-138; Gilde and Van Bilsen. 2003. Acta Physiol. Scand. 178: 425-434; Kersten, S. 2002. Eur. J. Pharmacol. 440: 223-234; Mudaliar and Henry. 2002. Curr. Opin. Endocrinol. Diabetes 9: 285-302). The PPARα isoform, predominantly involved in fatty acid and lipid catabolism and import, activates genes involved in fatty acid oxidation in the liver, heart, kidney, and skeletal muscles (Fruchart et al. 2003. Prog. Exper. Cardiol. 8: 3-16; Gilde and Van Bilsen, supra).
The pharmocological effects of PPARα agonists are well established. In the liver, activation of PPARα leads to increased β-oxidation of fatty acids and decreased triglyceride-VLDL (very low density lipoprotein) synthesis (Fruchart and Duriez. 2004. Ann. Pharmaceut. Franc. 62: 3-18). Activation of PPARα also leads to the reduction of triglyceride because of repression of hepatic apolipoprotein C-III and to the increase in lipoprotein lipase gene expression (Gervois et al. 2000. Clin. Chem. Lab. Med. 38: 3-11). Furthermore, PPARα activation causes induction of hepatic apolipoprotein A-I and A-II expression, in humans, leading to increased plasma HDL cholesterol.
Likewise, the clinical benefit of PPARα agonists with respect to CVD risk is well established. For example, a secondary prevention study, the Veterans Affairs High-Density Lipoprotein Intervention Trial (VA-HIT), demonstrated a significant 22% reduction in coronary heart disease (CHD) events during a median follow-up of 5.1 years by treating patients with PPARα agonist gemfibrozil (a fibric acid derivative), when the predominant lipid abnormality was low HDLc (Otvos, J. D., et al., Circulation. 2006; 113: 1556-1563). In the same study, gemfibrozil treatment increased total HDL particles (10%) as a result of increased numbers of small HDL particles (21%) offsetting reductions in large- and medium-size HDL subclass particles.
TRT with concomitant administration of a hypolipidemic agent such as a PPARα agonist can mitigate any T-induced decreases in apoA1 and HDL. Moreover, both T and PPARα agonists upregulate SR-B1, which mediates CE from large HDL particles. They both also upregulate hepatic lipase, which generates very small HDL particles resulting in greater CE mediated through ABCA1 receptor. Furthermore, PPARα agonists further enhance CE through an increase in ABCA1 transcriptional activity by up-regulating the receptor that is the only gateway for mediating CE via small HDL small particles.
There remains a need for pharmaceutical products that safely treat testosterone deficiency and symptoms thereof, which includes mitigating any negative impact T may have on cardiovascular outcomes. Described herein are pharmaceutical products that meet such need through reliance on the mechanistic synergy between oral T esters and hypolipidemic agents such as PPARα agonists whereby both agents act to increase serum concentration of anti-atherotic very small HDL particles, including preβ-1 HDL.